Kill the sharks, lose the shellfish, too

Removal of the apex predators in the Atlantic has had knock on consequences in …

It's not secret that we're overfishing the seas. Across the world, marine ecosystems are being depleted at a rate of knots in order to satisfy the demands of a global consumer society. The great sharks have been no exception. These apex predators have been the kings of their food webs since the time of the dinosaurs, the scourge of other sea life, and the darlings of the Discovery Channel. What they hadn't bargained on was the fact that some cultures quite like eating their fins. A consequence of this practice, along with bycatch from commercial fishing, has resulted in an almost total eradication of species such as the sandbar shark, the bull shark, scalloped hammerhead, tiger shark and others.

This interference with the existing marine food webs has had unforeseen knock-on consequences, according to new research from a team of marine biologists from Canada and US, published today in Science. Ransom Myers and colleagues have looked at the ecological impact of the removal of apex predators in the Atlantic ocean, and the results are not what you might think.

With the great sharks gone, their prey has a much easier time, and species such as the cownose ray have increased in numbers, by as much as eight percent a year. This has been bad news for shellfish, who have been devastated by the increase in ray numbers. North Carolina's bay scallop fishery has been wiped out, and shellfish stocks up and down the eastern seaboard of the US, the migration route of the cownose ray, are significantly down on historical levels.

I don't like to be too pessimistic, but I have to wonder how much longer we can keep up our levels of commercial fishing before we've totally exhausted the oceans. Thankfully, there are still fish which are sustainable, and guides exist for consumers in the US and UK to help guide our choices in a responsible direction.